The present invention relates to a data symbol reading apparatus for reading coded information, such as a data symbol, and, in particular, to a non-contact type data symbol reading apparatus. That is, a data symbol reading apparatus that is not brought into contact with a plane of the data symbol in the reading process. The present invention is particularly applicable to a data symbol reading apparatus for reading a two-dimensional data symbol, such as, a monochrome mosaic pattern.
In general, when a data symbol is to be read, the data symbol reading apparatus is brought into contact with a surface on which the two-dimensional data symbol is formed. The apparatus is arranged such that, in this position, an image of the data symbol is formed on a CCD (Charge Coupled Device) by an imaging lens. This arrangement is referred to as a contact type data symbol reading apparatus.
However, in order to increase the range of use of a data symbol reading apparatus, recent designs have been directed to a non-contact type data symbol reading apparatus in which the data symbol reading apparatus does not have to be brought into contact with the surface on which the two-dimensional data symbol is formed.
The non-contact type data symbol reading apparatus has the problem that, because there is no contact with the surface, the data symbol may not be sufficiently illuminated to provide an accurate reading. This problem is particularly important in the case of reading a two-dimensional data symbol which carries more information than a conventional bar-code data symbol in a similar area.
Further, if a more intense light source is used, the illumination of the data symbol may be non-uniform, also causing problems with the accuracy of reading the data symbol.